• 대한기계학회논문집
• /
• 제17권10호
• /
• pp.2391-2397
• /
• 1993

The distribution of fatigue crack growth rate is influenced by the measuring interval and methods of calculation of crack growth rate. The purpose of this paper is to suggest a method for the evaluation of crack growth rate distribution without the influence. The constant ${\Delta}P$ test and the constant .DELTA.K test are executed by using the CT specimen. The measuring interval of (${\Delta}a$/W=0.0067~0.014) crack length is not affected by methods of the calculation of the fatigue crack growth rate is suggested.

• 한국생산제조학회지
• /
• 제7권3호
• /
• pp.68-78
• /
• 1998

Welding structure contains residual stress due to thermal-plastic strain during welding process, and its magnitude and distribution depend on welding conditions. Cracks initiate from various defects of the weldment, propagate and lead to final fracture, The crack initiation and propagation processes are affected by the magnitude and distribution. Therefore, the magnitude and distribution of weldment residual stress should be considered for safety design and service of welding structures. Also it is very important that more accurate assessment method of fatigue crack growth must take into account the redistributing the residual stress quantitively. because the residual stress in weldment has characteristics of its redistribution with loading magnitude, number of cycles and fatigue crack propagation. In this study fatigue crack behavior of STS-304 weldment was investigated during crack propagation into tensile residual stress region or compressive residual stress region. Crack growth rates were predicted and compared with experimental results.

• 한국레이저가공학회지
• /
• 제9권2호
• /
• pp.1-9
• /
• 2006

In this paper, we investigated the characteristics of fatigue fracture on TB(Tailored Blank) weldment by comparing the fatigue crack propagation characteristics of base metal with those of TB welded sheet used for vehicle body panels. We also investigated the influence of center crack on the fatigue characteristic of laser weld sheet of same thickness. We conducted an experiment on fatigue crack propagation on the base metal specimen of 1.2mm thickness of cold-rolled metal sheet(SPCSD) and 2.0mm thickness of hot-rolled metal sheet(SAPH440) and 1.2+2.0mm TB specimen. We also made an experiment on fatigue crack propagation on 2.0+2.0mm and 1.2+1.2mm thickness TB specimen which had center crack. The characteristics of fatigue crack growth on the base metal were different from those on 1.2+2.0mm thickness TB specimen. The fatigue crack growth rate of the TB welded specimens is slower in low stress intensity factor range $({\Delta}K)$ region and faster in high${\Delta}K$ region than that of the base metal specimens. The slant crack angle slightly influenced the crack propagation of the TB specimen of 2.0+2.0mm thinkness.

• 대한기계학회논문집A
• /
• 제25권1호
• /
• pp.54-60
• /
• 2001

This study is to investigate the mechanical properties and the fatigue crack propagation of fire resistance steel for frame structure as the chemical composition was changed by addition of N, B and rolled end temperature was varied. We used two kinds of specimen, the one is parallel and the other is perpendicular to the rolling directions. As rolled end temperature increased, volume fraction of ferrite and pearlite decreased, but volume fraction of baintie and grain size increased. Micro-hardness decreased as rolled end temperature increased, but tensile and yield strength increased. Volume fraction of ferrite and pearlite decreased by addition of N. But volume fraction of bainite, tensile and yield strength increased. Microstructure was changed to martensite by addition of B, and tensile and yield strength increased. Fatigue life of TL direction specimen was shorter than that of LT direction specimen. There was no significant effect to fatigue crack propagation rate by addition of N and changing rolling condition, but fatigue life was increased by addition of B.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2004년도 추계학술대회 논문집
• /
• pp.725-728
• /
• 2004

In this study, the effect of mode II by variation of multilevel loading direction was experimentally investigated in the fatigue crack propagation behavior. To generate mixed-mode I+II loading state, the compact tension shear(CTS) specimen and loading device were used in this tests. The experimental method divided into three steps and three cases that were step I(0$^{\circ}$), step II(30$^{\circ}$, 60$^{\circ}$, 90$^{\circ}$),step III(0$^{\circ}$) and case I(0$^{\circ}$ ⇒ 30$^{\circ}$ ⇒ 0$^{\circ}$), case II(0$^{\circ}$ ⇒ 60$^{\circ}$ ⇒ 0$^{\circ}$), case III(0$^{\circ}$ ⇒ 90$^{\circ}$ ⇒ 0$^{\circ}$). The result of test, the step II affected to the step III in the all case. Specially, The fatigue crack propagation rate was faster and the fatigue life was smaller than of mixed mode I+II(30$^{\circ}$,60$^{\circ}$) due to the effect of mode II in the step III of the case III

• 대한기계학회논문집
• /
• 제12권3호
• /
• pp.473-480
• /
• 1988

본 연구에서는 용접잔유응력의 영향을 보다 정확하게 규명할 목적으로 용접잔 유응력의 피로반복 사이클 수에 따른 이완량을 측정하고, 모재의 실험 결과에 중첩의 개념을 도입함으로써 용접잔유응력이 피로크랙 전파에 미치는 영향을 규명할 수 있는 방법을 제시한다. 하나의 예로서 SS41재를 선택하여 서브머지드아크 용접을 한 후, 본 논문의 방법을 작용함으로써 용접잔유응력의 영향에 대하여 분석하였다.

• 수산해양기술연구
• /
• 제28권3호
• /
• pp.286-294
• /
• 1992

In this paper, the corrosion fatigue crack propagation behavior of structure rolled steel (SWS 41C) was investigated by changing the thickness, and this experiment was done by the three point bending corrosion fatigue tester. The main results obtained are as follows: 1) As the thickness of specimen becomes thicker, the corrosion sensitivity to initial stage crack becomes some sensitive, and that the fatigue life becomes more sensitive. 2) The crack growth rate to initial stage crack (da/dN) was retarded as the thickness of specimen becomes thicker. But after initial stage crack, as the thickness of specimen is more thicker, da/dN is more rapid. 3) As the corrosion fatigue crack length grows, the accelerative factor of thick specimen (t=12mm) is more higher than that of thin specimen (t=6mm). 4) As the corrosion fatigue crack length grows, the corroson potential of both thick specimen and thin specimen becomes more less noble potential, however thick specimen (t=12mm) tends to more less noble potential than that of thin specimen(t=6mm).

• 대한기계학회논문집A
• /
• 제21권7호
• /
• pp.1097-1105
• /
• 1997

Because of the existence of stress interaction field made by other defects and propagating cracks, the structure may be weakened. Therefore in this study, the crack behavior in the interaction field made by two different cracks is studied experimentally. In the experiment, vertical distance between two cracks and applied stress are varied to make different stress interacted field. In addition, the effect of plastic zone is used to examine crack propagation path and rate. Three types of crack propagation in the interacted field were found, and crack propagating path and rate of two cracks were significantly changed according to different applied stress as each crack propagates. And the results are attributed to the effect of the size and shape of the plastic zone.

• 대한기계학회논문집
• /
• 제16권7호
• /
• pp.1373-1380
• /
• 1992

본 연구에서는 전보에서 실험역학적으로 도출한 .DELTA.A가 재료 및 하중크기에 의존하는 점에 착안하여, SNC631-A, SNC631-B, S45C, A12024-T3 및 A17075-T6 등 5종 류 재료를 응력비 R=0.1, 0.3, 0.5에서 피로크랙전파속도시험을 실시하고, 피로크랙팁 의 국소피로변형률장의 상태를 정량적으로 나타낼 수 있는 피로변형률확대계수 .DELTA.A(m, P)를 이용하여 크랙전파속도 da/dN을 통일적으로 평가하고, 그 결과의 유용성을 명백 히 하였다.

• 대한조선학회논문집
• /
• 제44권4호
• /
• pp.417-424
• /
• 2007

With regard to corrosion fatigue crack initiation life (Nc), it has been treated ambiguously for the member which doesn't have stress concentration area. In this research, in order to clarify the corrosion fatigue crack initiation life (Nc), corrosion fatigue tests were carried out. Reasonable and universal corrosion fatigue crack initiation life (Nc) was defined and corrosion fatigue crack initiation/propagation model was suggested also. As the fatigue crack which emanates from the pit is usually small, accordingly it is treated as a small crack. In addition, the observation of the corrosion fatigue fracture surfaces using SEM was conducted. And the fracture mechanics analysis using an intrinsic crack model was conducted for the treatment of the small crack. Finally, the followings were obtained. When there is no clear stress concentration point which seems to fall into a corrosion fatigue crack initiation life, the significance of the definition and suggestion of the moment of the reasonable and universal corrosion fatigue crack initiation life (Nc), at which the fatigue crack propagation rate becomes faster than the corrosion pit growth rate so that the fatigue crack initiates from the pit and propagates in earnest, has been clarified.